Sharks: Is extinction over the horizon?

Lemon sharks are among the species tagged by biologists at the Kennedy Space Center. Photographed in the shallow waters off Cape Canaveral Air Force Station, these stocky and powerful sharks are named for their yellow color.(Photo: InoMedic Health Applications)

The lagoon and other coastal nursery habitats for sharks are reeling from pollution, fishing pressure and other threats. Sharks that survive to adulthood then face an ocean of troubles, from fishermen seeking an adrenaline rush to others after fins for $100 bowls of soup.

"We're killing about 6 ½ to 8 percent of the sharks out there per year," said Boris Worm, professor of marine biology at Dalhousie University in Nova Scotia.

Shark reproduction, even at its best, can't keep pace with shark deaths. Most shark species are losing ground, including many that roam the Space Coast. Some could face extinction within a decade or two.

And while sharks might not exactly tug at our heartstrings like dolphins and other more cuddly creatures, think about those scallops or that lobster you enjoy. Sharks play such an integral role in the food web that if they vanish, the effect could be felt on your dinner plate.

An estimated 100 million sharks are killed annually, Worm and other researchers estimate, 20 million or more per every fatal shark attack.

And that wholesale slaughter could already be sending dire consequences cascading down the food chain, much to the bane of scallop and lobster lovers.

"What we're finding is that for some of these big species, if you don't have them, you're going to be in trouble," said Michael Heithaus, marine biologist at Florida International University.

He likens the ecological effects to how wolf declines enabled deer population booms.

Researchers suspect the collapse of some lobster and scallop fisheries in recent decades might have been due, in part, to shark declines. The theory: With fewer sharks to eat them, octopuses that feast on spiny lobster can flourish. And rays — no longer fodder for sharks — are free to gobble up bay scallops at will.

In western Australia, fewer tiger sharks resulted in more sea turtles, Heithaus said, and other grazing species that denuded marine plants, the foundation of the food web.

"Without those sharks, you can wipe out large swaths of seagrass beds," Heithaus said.

Shark declines can trigger coral loss, as well. Fish spread disease to larger areas of the reef when fewer sharks are around to keep them in check.

So to better protect sharks, scientists want to know more about their life cycles. By identifying crucial nursery grounds, they hope to improve federal management of large coastal sharks.

But recoveries for many shark species could require decades, because many take 20 years or more to reach reproductive age and have small litters, every other year or so.

Scalloped hammerheads are among the most imperiled. Foreign vessels target them for their high-priced fins, which are used in soups that can cost more than $100 a bowl. The species is easy to catch in large numbers because it schools together. The meat is considered unpalatable. But the fins are so valuable that fishermen dump the rest of the shark at sea to die, making room for more fins.

Scalloped hammerheads and many other sharks also are killed as "by-catch" in fisheries targeting other species.

Last month, the federal government listed four key populations of scalloped hammerhead sharks under the Endangered Species Act. The move didn't include scalloped hammerheads off Florida's east coast and in the Gulf of Mexico, where strict fishing rules already exist.

Habitats threatened

While finning is rare — and illegal — off Florida, scientists say the bigger problem here is the drastic drop in lagoon seagrass which has stressed one of the most vital shark nursery habitats.

"The seagrass is the basis of the food chain," Gilmore said. "The food resources have really gone down substantially."

Among the lagoon sharks potentially in peril:bull sharks, scalloped hammerheads and sawfish, to name a few.

The Indian River Lagoon is the most vital nursery habitat for bull sharks on the Atlantic east coast. Large pregnant bull sharks, some upward of 8-feet long, enter the lagoon through Sebastian Inlet and other inlets, usually between May and August. They typically don't eat while in the lagoon but just give birth to their pups and exit the estuary, unbeknownst to swimmers and waders.

Despite the bull shark's reputation as among the most dangerous offshore, there's never been a documented shark attack in the 156-mile-long lagoon.

Paul Lorenzen, 49, of Melbourne, caught a 6-footer in Sebastian River a few years ago. Around the same time, Jeremy Wade, host of the hit show, "River Monsters," landed a similar-sized bull shark in the lagoon near Fort Pierce.

Lorenzen always has bulls on his mind when he enters the lagoon — with respect.

"I like to wade in the river," he said. "My knees is as high as I go, because you just never know."

Scalloped hammerheads and lemon sharks are also known to enter the lagoon, but mostly near inlets.

Another lagoon dweller, the sawfish — an intermediate between sharks and rays — is the Rodney Dangerfield of the shark world. These lowly "flat" sharks garner much less press, fear or respect. But they are among the most endangered shark-like species, and the strangest.

This odd-looking creature swims through schools of mullet, swiping its saw side-to-side, stunning fish to make them easy eating.

Sawfish can grow more than 20 feet and were once commonplace in the lagoon. They have all but vanished from overfishing. While classified as rays, they're primarily shark-like in appearance and closely related to sharks.

In the 1800s, net fishermen wanted to rid the lagoon of sawfish because they ruined nets.

"Some fishermen caught well over 100 sawfish in a single season," Gilmore said.

Fact: Though sometimes considered mammals, like dolphins, they are like any other fish. They depend on gills that allow them to breathe while underwater.

Wilder Monterey Bay Aquarium handout

Sharks are older than dinosaurs

Fact: They are geezers. Some data indicate that sharks have been on Earth for more than 420 million years. That likely would make them senior to dinosaurs.

AP photo

Sharks are smooth and slimy

Fiction: Most shark skin is rough, sand paper rough. That offers it protection from other sharks. In fact, shark skin was once used as sand paper and also for sword grips.

Fischer Productions

Sharks have walnut-size brains and thus aren't very smart

Myth: Well, you can say that about a lot of animals - and probably people. Brain size varies among sharks but sharks are known to demonstrate complex social arrangements, some living in groups and hunting in packs. Their brain-to-body ratio is similar to birds and mammals.

Discovery Channel

All sharks must swim constantly

Mostly fact: Most sharks do need to swim continuously in order to pass water over their gills and breathe, some sharks are able to actively pump water over their gills while resting on the sea floor.

Getty Images

Shark fins grow back if they are cut off

Myth: A finned shark soon becomes a dead shark. A finned shark will drown, bleed to death or be eaten by other sharks. Seems like waste. Many say shark fins are flavorless and have no nutritional value. Each year, tens of millions of sharks are killed for their fins.

Getty Images

There are 100 species of sharks

Myth: There are at least 500 shark species.

Getty Images

Sharks don't use their teeth for chewing

Fact: That's true. Sharks use their teeth to grab hold of their prey and then tear the flesh. It's also called "gripping and ripping."

Getty Images

Sharks are close to extinction

Mostly myth: While the the global population is believed to be declining, only 20 percent to 30 percent of sharks are believed to be close to extinction. They include the Great Hammerhead, Scalloped Hammerhead and Smooth Hammerhead.

Getty Images

If a shark attack has not occurred, it means they do not live in that area

Myth: Wishful thinking. Sharks inhabit all of the world's oceans - from inshore, coastal waters to the open sea - and some can even be found in freshwater rivers and lakes.

Getty Images

Sharks have a good sense of smell but poor vision

Myth: No question about the sense of smell but sharks also have good eyesight, and color vision. Shark eyes have a large, orb lens, a cornea, a retina (with both rods and cones), an iris and a pupil. Their vision is even pretty good in dim light. Sharks, like cats who also see well in dim light, have a mirror-like layer in the back of the eye called the tapetum lucidum.

AFP / Getty Images

Aside from humans, sharks really don't have any enemies

Myth: Killer whales will occasionally eat sharks. But smaller killers - parasites - are responsible for numerous shark deaths annually. And keep in mind that sharks often eat other sharks. Bull and tiger sharks particularly are known for this. And some sharks, if they're hungry enough, will kill and eat their own pups.

Getty Images

Sharks give birth, like mammals

Fact: Some shark species are oviparous, meaning they drop eggs. Others are viviparous and give birth to live young. With the live-bearing species there is a placenta like humans have. With the latter, shark embryos get their nutrition from a yolk sac or unfertilized egg capsules.

Getty Images

Sharks rarely poke their head above water

Mostly fact: Of all the species of sharks, the 'Great White' is really the only one that bring its head above water. There really is health benefit to doing so but researchers have a couple of theories. First, they believe it allows them to search for larger prey that can be above water and not paying attention to them. Second, it can be for them to further show their dominance since they are extremely aggressive by nature.

When sharks lose their teeth, they can't hunt or eat

Myth: Sharks, with the most powerful jaws on the planet, likely never run out of teeth. When one is lost another moves forward from the rows of backup teeth. A shark may use over 20,000 teeth during its life. That's a lot of necklaces.

Getty Images

Sharks are cold blooded

Mostly fact: The Great White and Mako are considered warm-blooded, or endothermic. This means it controls its own body temperature internally rather than being fully dependent on the temperature of its surroundings. This is unusual for a fish and not many sharks have this characteristic.

Getty Images

Sharks can't get cancer

Myth: Because sharks very rarely get cancer, scientists study their cartilage in the hopes of finding a cure for the disease.

Getty Images

Sharks are sexists when it comes to eating

Fact: Even though almost equal numbers of men and women spend time in the ocean, no one knows why sharks seem to prefer to attack men. In fact, nearly 90 percent of shark attack victims are male.

Courtesy Ocearch

Sharks can swim perilously close to shore

Fact: As long as a shark's back is mostly under water, it can swim easily. A nine-foot-long bull shark can swim in just two feet of water. About two-thirds of shark attacks on humans have taken place in water less than six feet deep.

Getty Images

Sharks, like fish, have a swim bladder that keeps them afloat

Myth: Sharks instead have a large oil-filled liver, and sharks that spend a lot of time on the surface, such as whale and basking sharks, have a massive liver. Shark liver oil used to be the main source of vitamin A for humans.

Getty Images

Sharks are always looking for their next meal

Myth: Sharks, like lions and other predators, usually kill only when they are hungry. Some sharks can live a year without eating, living off the oil they stored in their bodies.